A Cost Analysis of Switching Calcium Channel Blockers: Study Design

In: Main

2 Jul 2010

This study was a retrospective utilization and cost analysis based on the records of patients using pharmacy services at Martin Army Community Hospital in Fort Benning, Georgia, who had been prescribed in the past and were switched to either felodipine ER or nifedipine CC beginning in January of 1999.

All patients using the Martin Army Pharmacy who had been dispensed amlodipine were advised to have their physicians convert them to either felodipine ER or nifedipine CC beginning in January of 1999.

Physicians were also given the option of maintaining patients on amlodipine through a special purchase request program. Physicians within the hospital could request that their patients remain on amlodipine by presenting justification in writing to the P&T committee for review. The P&T committee had developed criteria to justify a patient remaining on amlodipine and authorized the hospital pharmacy to oversee the program. Thus, the pharmacy could authorize amlodipine if the patient met any of the following criteria: previous therapy failure caused by a lack of efficacy or documented adverse events to felodipine ER or  CC; concomitant angina or coronary heart disease; or blood pressure that was controlled with amlodipine after multiple failures with other medications. All other special requests were reviewed by a physician/pharmacist review board. The relatively stringent criteria for maintaining patients on canadian amlodipine raises the possibility that they might have had more severe or complicated form of the disease than patients switched to felodipine ER or nifedipine CC. Nevertheless, the actual costs for treating these patients, rather than other historical data, were used for comparison with results from patients who changed their antihy-pertensive medications.

Selection of Records for Review

A computerized list was generated to determine all patients who had received a prescription for amlodipine in November or December of 1998. The list included 1,379 patients on amlodipine. Three hundred seventy-two patients were selected for evaluation using a table of random numbers. Eligible patient records, coded by specific patient identifier, were then retrospectively analyzed from the time of the conversion, beginning in January of 1999, through a one-year period ending in the early spring of 2000. Data were extracted and recorded using standardized forms developed for this study.

Data Collected

Data retrieved from each patient record included demographic characteristics, amlodipine dosage prior to conversion, and any use of concomitant cardiovascular (CV) medication pre-conversion,  ER or nifedipine CC dose at conversion, changes in dosing or discontinuation of therapy within one year of post-conversion, and the number of concomitant CV medications used post-conversion. Concomitant medications were defined as prescription medications other than amlodipine, felodipine ER, or medication nifedipine CC prescribed for chronic CV-related illness. Concomitant CV medications were divided into eight classes: diuretics; p-blockers; angiotensin-converting enzyme (ACE)-inhibitors; CCBs other than amlodipine, felodipine ER, or nifedipine CC; a-blockers; angiotensin-receptor blockers; nitrates; and other antihypertensive agents.

It was assumed that patients whose records were reviewed were receiving all their CV medications from the pharmacy at Martin Army Community Hospital. It was also assumed that all patients taking a nitrate medication had a diagnosis of angina pec-toris in addition to hypertension.

Medication Costs

Medication costs were based on the federal supply schedule (FSS) price for each medication at the time of analysis.

Statistical Analysis

Cost data prior to and after switching, requirements for CV-related concomitant medications, and total daily treatment costs were analyzed using paired ttests. Independent ttests were used to compare results from patients switched to canadian felodipine ER or nifedipine CC with those from patients maintained on amlodipine.

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